doc: add undici notes

Refs: nodejs#38533

doc/api/http.md

@@ -54,6 +54,8 @@ list like the following:
 added: v0.3.4
 -->
 
+XXX: UNDICI
+
 An `Agent` is responsible for managing connection persistence
 and reuse for HTTP clients. It maintains a queue of pending requests
 for a given host and port, reusing a single socket connection for each
@@ -375,6 +377,8 @@ added: v0.1.17
 
 * Extends: {Stream}
 
+XXX: UNDICI
+
 This object is created internally and returned from [`http.request()`][]. It
 represents an _in-progress_ request whose header has already been queued. The
 header is still mutable using the [`setHeader(name, value)`][],
@@ -2705,6 +2709,8 @@ changes:
     description: The `options` parameter can be a WHATWG `URL` object.
 -->
 
+XXX: UNDICI
+
 * `url` {string | URL}
 * `options` {Object} Accepts the same `options` as
   [`http.request()`][], with the `method` always set to `GET`.
@@ -2824,6 +2830,8 @@ changes:
     description: The `options` parameter can be a WHATWG `URL` object.
 -->
 
+XXX: UNDICI
+
 * `url` {string | URL}
 * `options` {Object}
   * `agent` {http.Agent | boolean} Controls [`Agent`][] behavior. Possible

doc/api/https.md

@@ -22,6 +22,8 @@ changes:
                  sessions reuse.
 -->
 
+XXX: UNDICI
+
 An [`Agent`][] object for HTTPS similar to [`http.Agent`][]. See
 [`https.request()`][] for more information.
 
@@ -212,6 +214,8 @@ changes:
     description: The `options` parameter can be a WHATWG `URL` object.
 -->
 
+XXX: UNDICI
+
 * `url` {string | URL}
 * `options` {Object | string | URL} Accepts the same `options` as
   [`https.request()`][], with the `method` always set to `GET`.
@@ -268,6 +272,8 @@ changes:
     description: The `options` parameter can be a WHATWG `URL` object.
 -->
 
+XXX: UNDICI
+
 * `url` {string | URL}
 * `options` {Object | string | URL} Accepts all `options` from
   [`http.request()`][], with some differences in default values:

doc/api/zlib.md

@@ -141,40 +141,32 @@ tradeoffs involved in `zlib` usage.
 ```js
 // Client request example
 const zlib = require('zlib');
-const http = require('http');
+const undici = require('undici');
 const fs = require('fs');
-const { pipeline } = require('stream');
+const { pipeline } = require('stream/promises');
 
-const request = http.get({ host: 'example.com',
+const { body, headers } = await undici.request({ host: 'example.com',
                            path: '/',
                            port: 80,
                            headers: { 'Accept-Encoding': 'br,gzip,deflate' } });
-request.on('response', (response) => {
-  const output = fs.createWriteStream('example.com_index.html');
-
-  const onError = (err) => {
-    if (err) {
-      console.error('An error occurred:', err);
-      process.exitCode = 1;
-    }
-  };
 
-  switch (response.headers['content-encoding']) {
-    case 'br':
-      pipeline(response, zlib.createBrotliDecompress(), output, onError);
-      break;
-    // Or, just use zlib.createUnzip() to handle both of the following cases:
-    case 'gzip':
-      pipeline(response, zlib.createGunzip(), output, onError);
-      break;
-    case 'deflate':
-      pipeline(response, zlib.createInflate(), output, onError);
-      break;
-    default:
-      pipeline(response, output, onError);
-      break;
-  }
-});
+const output = fs.createWriteStream('example.com_index.html');
+
+switch (headers['content-encoding']) {
+  case 'br':
+    await pipeline(body, zlib.createBrotliDecompress(), output);
+    break;
+  // Or, just use zlib.createUnzip() to handle both of the following cases:
+  case 'gzip':
+    await pipeline(body, zlib.createGunzip(), output);
+    break;
+  case 'deflate':
+    await pipeline(body, zlib.createInflate(), output);
+    break;
+  default:
+    await pipeline(body, output);
+    break;
+}
 ```
 
 ```js